1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for fabricating an LCD device, and more particularly, to a liquid crystal spraying apparatus that can uniformly dispense liquid crystal to improve the image quality of the LCD device.
2. Discussion of the Related Art
With the development of various portable electronic devices such as mobile phones, PDAs (personal digital assistant), notebook computers, and the like, the demand for flat panel display devices (that are thin, small and lightweight) has recently increased. Various display devices, such as liquid crystal display (LCD) devices, plasma display panels (PDP), field emission displays (FED), and vacuum fluorescent displays (VFD), have been actively studied for use as a flat panel display device. Among these various display devices, LCD devices are being spotlighted as the preferred flat panel display devices because of their simplicity in mass-production, facile driving method and high-resolution image.
An LCD device displays information on its screen by using refractive index anisotropy of liquid crystal. The LCD is generally constricted to include a lower substrate on which a thin film transistor (TFT) and a pixel electrode are formed, an upper substrate on which a color filter layer is formed, and a liquid crystal layer interposed between the lower and upper substrates.
A method for fabricating an LCD device is divided into an array substrate forming process for forming a lower substrate, a color filter substrate forming process for forming an upper substrate, and a cell process. These processes will now be described with reference to FIG. 1.
FIG. 1 is a flowchart illustrating a method for fabricating an LCD device according to the related art.
Referring to FIG. 1, a plurality of gate lines and data lines defining a plurality of pixel regions are formed on a lower substrate, and a TFT, which is a driving device connected to the gate line and the data line, is formed in each pixel region (S101) through the array substrate forming process. A pixel electrode is also formed through the array substrate forming process, which is connected to the TFT and drives a liquid crystal layer according to a signal applied thereto via the data line.
An R/G/B color filter layer and a common electrode are formed on a upper substrate (S104) through the color filter substrate forming process.
Thereafter, alignment layers are respectively coated on the upper and lower substrates, and then the coated alignment layers are rubbed to provide an anchoring force or surface force (that is, a pretilt angle or an alignment direction) to the molecules of a liquid crystal layer to be formed between the upper and lower substrates (S102, S105).
Thereafter, spacers are dispersed on the lower substrate to maintain a constant cell gap, a sealant is coated on an outer portion of the upper substrate, and then the upper and lower substrates are pressed together (S103, S106, S107).
Large-size glass substrates are generally used for the upper and lower substrates. Because a plurality of liquid crystal panel regions are formed on the large-size glass substrates and a TFT and a color filter layer are formed on each of the liquid crystal panel regions, the assembled substrates should be cut and processed to fabricate a plurality of liquid crystal panels (S108).
Thereafter, a liquid crystal layer is formed in each of the liquid crystal panels by injecting liquid crystal into the liquid crystal panel through a liquid crystal injection hole thereof and sealing the liquid crystal injection hole. The injection is achieved by a pressure difference between a vacuum chamber 10 and the liquid crystal panel 11 (see FIG. 2). The method for fabricating an LCD panel is completed by inspecting the liquid crystal panel (S109, S110).
FIG. 2 is a schematic view illustrating an apparatus for injecting liquid crystal into a liquid crystal panel according to the related art.
Referring to FIG. 2, a vessel 12 filled with liquid crystal 14 is provided in a vacuum chamber 10, and a liquid crystal panel 11 is positioned over the vessel 12. The vacuum chamber 10 is connected to a vacuum pump, and thus the inside of the vacuum chamber 10 is maintained at a set level of vacuum when liquid crystal is injected into the liquid crystal panel 11. Also, a moving unit (not shown) is installed in the vacuum chamber 10, which brings an injection hole 16 at the bottom of the liquid crystal panel 11 into contact with the liquid crystal 14 in the vessel 12 by moving the liquid crystal panel 11 down from a higher position. This method is called a vacuum/dipping injection method.
The degree of vacuum in the vacuum chamber 10 is reduced by supplying nitrogen gas into the vacuum chamber 10 while the injection hole 16 is in contact with the liquid crystal 14. The liquid crystal 14 is then injected through the injection hole 16 into the liquid panel 11 by means of a pressure difference between the inside of the liquid crystal panel 11 and the vacuum chamber 10. The method for forming a liquid crystal layer in the liquid crystal panel 11 is completed by sealing the injection hole 16 with a sealant after completing the injection of the liquid crystal 14 into the liquid crystal panel 11.
However, the method of forming the liquid crystal layer by injecting liquid crystal 14 into the liquid crystal panel 11 in the vacuum chamber 10 has the following problems.
First, the process time for injecting liquid crystal 14 into the liquid crystal panel 11 is long. In general, because a cell gap between the array substrate and the color filter substrate in a liquid crystal panel is very small (about several μm), a very small amount of liquid crystal is injected into the liquid crystal panel per unit time. For example, about 8 hours are required to complete the injection of liquid crystal into a 15-inch liquid crystal panel. The long injection time decreases productivity (or yield).
Second, a large portion of the liquid crystal 14 used for the liquid crystal injection process is discarded. That is, only a very small amount of the liquid crystal 14 in the vessel 12 is actually injected into the liquid crystal panel 11. Because the liquid crystal 14 can be degraded by the impurities in the injection apparatus and the gases used as well as by the impurities generated when the liquid crystal 14 comes into contact with the liquid crystal panel 11, the remaining liquid crystal 14 in the vessel 12 after dipping a single liquid crystal panel 11 should be discarded and may not be used for other liquid crystal panels. This increases fabrication costs.